CH-PS 612,736 describes a small fan having a fan wheel with radially acting vanes. Moreover, the fan wheel has permanent magnets at the location of the air gap to form poles of alternating polarity along the air gap in the circumferential direction. At the location of the air gap the permanent-magnetic poles of the rotor, which are disposed in a radial plane, are situated opposite stator poles which are arranged in radial planes and which can be energized by coils. When the coils are energized electric fields are produced in the air gap and exert a torque on the rotor.
This construction is intricate because in addition to the fan wheel permanent magnets are required. On account of the principle used it is required to detect the position of the fan wheel for the energization of the coils. Moreover, the use of the permanent magnets as shown limits the maximum speed and the temperature to values restricting the field of use.
Since with vacuum cleaners the power consumption is still a typical indication of their efficiency, vacuum cleaners employ comparatively efficient separate motors to drive a separate impeller. Generally, the mounting volume of such a unit comprising an impeller and a motor is comparatively large. Recently, the manufacturers have begun to specify not only the power consumption of the appliance but also its suction power at the nozzle.
Conventional vacuum cleaners also have the disadvantage that the separate construction of the impeller and the motor is in conflict with appliance miniaturization. At a speed of the order of magnitude of 25,000 r.p.m. there is a distinct noise production, which is mainly caused by the brushes of the universal motors which are used. The poor efficiency of the currently used units results in considerable heating of the motor. In order to carry off this dissipated heat the suction air stream is passed through or over the motor. This results in additional flow noise and flow losses.